The present invention is concerned with an antacid material prepared from magnesium oxide/hydroxide and aluminum sulfate and with the preparation thereof.
Aluminum and magnesium hydroxides, especially in gel form, have proved to be effective antacids in the treatment of gastric hyperacidity and of ulcers.
However, the preparation of a practically useful antacid based upon aluminum magnesium hydroxide comes up against considerable difficulties since a large variety of influences have a negative effect upon the effectiveness or compatibility. An excess, in the physiological sense, of magnesium hydroxide, for example, gives rise not only to a rapid increase of the pH value of the gastric juice above the neutral point and thus induces a rebound effect, i.e. a really excessive production of acid, but also exerts a strongly laxative action. An excess of aluminum hydroxide, on the other hand, usually gives rise to undesirable constipation.
In the case of conventional precipitation methods bases, for example sodium hydroxide, are also employed, the cations of which cannot be completely removed from the voluminous gels by washing out and, consequently, these cations manifest their own undesired actions. However, sodium ions in particular must not be present in cases of high blood pressure and of diseases of the kidney and heart.
Because of the harmful effects of sodium ions, an attempt has been made, according to U.S. Pat. No. 4,105,579, to obtain aluminum hydroxide gel in pure form by precipitation from aluminum salts with an aqueous solution of magnesium carbonate and subsequent filtration. In this manner, it is admittedly possible to obtain a sodium-free aluminum hydroxide gel but, for the above-mentioned reasons, it cannot be used directly as an antacid but must be admixed with a proportion of magnesium hydroxide.
According to Federal Republic of Germany Patent Specification No. 2,327,768, aqueous ammonia is used as a precipitation agent for the preparation of aluminum hydroxide. However, this process only apparently solves the problem since ammonium ions are also physiologically undesirable and, in the same way as alkali metal ions, are stubbornly held by the gel.
As is also known from Federal Republic of Germany Patent Specification No. 1,617,277 (column 2, lines 55-63), it is extremely difficult to dry aluminum and magnesium hydroxide gels without losing a considerable part of acid-binding activity. In the case of aluminum hydroxide gels, this disadvantage is even regarded as being a characteristic.
It is an object of the present invention to provide an antacid material which, apart from aluminum and magnesium, contains no other cations and, in a dry state, even after comparatively prolonged storage, does not lose its acid-binding buffering capacity and which has an unusually long period of action, without deviating from the ideal buffer zone of from about pH 3 to pH 5 at any time during the treatment therewith.
This object is, surprisingly, achieved by using solid magnesium hydroxide and/or magnesium oxide for precipitating an antacid from an aqueous solution of aluminum sulfate [Al.sub.2 (SO.sub.4).sub.3 ], the product obtained, after the removal of water-soluble components, being isolated in known manner and, if desired, dried.
The starting materials are used in an atomic ratio of magnesium to aluminum of 1:1 to 3:1 and preferably to 1.3:1 to 2:1.
The precipitation reaction is finished when the reaction mixture has reached a pH value of from 4.0 to 8.0 and preferably of from pH 5.0 to pH 8.0.
According to U.S. Pat. No. 3,239,416, an attempt has already been made to react a basic aluminum chloride [Al.sub.2 (OH).sub.2 Cl.sub.4 or Al.sub.2 (OH).sub.5 Cl]with appropriate non-toxic alkaline earth metal compounds. However, due to the presence of hydroxyl groups in the aluminum complex, a cross-linking in the end product is only partly possible. Consequently, a gel-like precipitate, a so-called co-gel, is obtained, the properties of which differ considerably from those of the end product obtained according to the present invention and which, in addition, must be freed from undesired chloride ions by repeated and laborious washing. Furthermore, in order to achieve a suitable pH value for the reaction, the addition of sodium carbonate or sodium bicarbonate is usually necessary when carrying out this known process.
A similar proposal, which by-passes the object of the present invention, has also been disclosed in Chemical Abstracts, 83, 84853E (1975). In this case, too, a pre-hydrolysed polybasic aluminum sulfate of limited reactivity is reacted with magnesium hydroxide. Due to the hydrolysis of sodium bicarbonate, undesired sodium ions are entrained which can scarcely be removed from the resultant gel.
In U.S. Pat, No. 4,105,579, a process is described for the preparation of a more or less pure aluminum hydroxide by precipitation from aluminum chloride solutions (or, alternatively, also nitrate and sulfate) by means of an alkaline earth metal carbonate, undesired amounts of carbonate thereby getting into the end product.